1. Field of the Invention
The field of the invention comprises, in general, devices which control vibration of buildings caused by seismic disturbances. In particular, the field of invention relates to air spring devices adapted to dampen vertical vibrations in buildings.
2. Description of the Prior Art
In order to protect a building from horizontal vibration, it is known to isolate the building superstructure from its base slab or foundation by interposing rolling members therebetween to permit the building superstructure to shift horizontally relative to its slab or foundation, thereby dissipating the energy of seismic vibration.
Since the average earthquake is mainly characterized by horizontal vibrations, the above-described isolation device can substantially cope with horizontal seismic shock. However, in the case of a large-scale structure located at the epicenter of an earthquake, it is quite possible that the structure will experience vertical, as well as horizontal vibrations which, if not controlled, could cause structural damage.
Vertical vibration control devices are generally known in the prior art, comprising vertically-expanding air springs. However, prior art vertically expanding and contracting air springs possess little inherent capability to resist horizontal deflection. As a consequence, when a structure is subjected to both horizontal and vertical vibrations, a rocking, or similar, very unstable motion results that renders the air springs ineffective to control vertical vibration. Air springs are comprised of telescoping canisters. The greater the overlap of canister side walls, the greater is the resistance to lateral deflection. However, as the resistance to lateral deflection is increased the capacity of the air spring to dampen vertical vibrations is decreased.